ABSTRACT
Toxic substance models attempt to model the fate and effect of toxic substances in ecosystems. They are most often biogeochemical models, because they attempt to describe the mass flows of the considered toxic substances, although there are models of the population dynamics, which include the influence of toxic substances on the birth rate and/or the mortality, and therefore should be considered a toxic substance model. This class of models considers the flow of toxic substance through the food chain or food web. Such models will be relatively complex and contain many state variables. Population dynamic models may include two or more trophic levels and ecotoxicological models will include the influence of the toxic substance concentration on natality, mortality and interactions between these populations. The application of pesticides implies that toxic substances are spread in nature. This includes the zero trophic level, which is understood as the medium - either soil, water or air.
